1. Field of the Invention
The present invention generally relates to spinning up a spindle motor in a hard disk drive. More particularly, the present invention relates to a disk drive employing a method of spinning up a spindle motor including detecting back electromotive force (BEMF) polarity change for selecting an initial commutation state for the spindle motor.
2. Description of the Prior Art
A huge market exists for hard disk drives for mass-market host computer systems such as M servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive must be relatively inexpensive, and must accordingly embody a design that is adapted for low-cost mass production. In addition, it must provide substantial capacity, rapid access to data, and reliable performance. Numerous manufacturers compete in this huge market and collectively conduct substantial research and development, at great annual cost, to design and develop innovative hard disk drives to meet increasingly demanding customer requirements.
In hard disk drives, data is stored on magnetic media disks in concentric data tracks, which are divided into groups of data sectors. Disks are typically stacked on a spindle assemble. The spindle assembly is mechanically coupled to a spindle motor which rotates the disks at a substantially constant operating spin-rate. The hard disk drive performs a spin-up operation to bring previously stopped disks to the operating spin-rate. There exists substantial competitive pressure to develop mass-market hard disk drives having faster spin-up operations to more quickly begin reading from and/or writing to the magnetic disks after the disks are spun-down to zero or other spin-rate lower than the operating spin-rate, especially after power-on of the computer system that employs the hard disk drive.
A spindle motor driver typically drives the spindle motor. A typical three-phase spindle motor includes a stator having three windings and a rotor. The rotor has magnets that provide a permanent magnet field. The spindle motor generates torque on the rotor when current flows through at least one of the windings. The torque depends on upon the magnitude and direction of current flow through the windings and an angular position of the rotor relative to the stator. The functional relationship between torque and current flow and angular position is commonly depicted in a set of torque curves, each of which corresponds to a respective one of a set of commutation states.
Conventional spin-up operations in hard disk drives include a cogging operation which cogs or prepositions the rotor at a fixed angular phase position. The following example conventional spin-up operation data is provided for an example multi-platter disk drive. The cogging operation is performed at zero revolutions per minute (RPM) spin-rate. An example cogging operation takes approximately 1.3 seconds. A blind table operation, where the velocity of the spindle motor is not monitored, typically is performed for approximately 0.3 seconds from 0 to approximately 400 RPMs. The blind table operation starts the rotor at the cogged fixed angular position and a corresponding predetermined initial commutation state is used to initially a control the spindle motor to generate a positive torque to move the disks in a forward direction. At approximately 400 RPMs, an approximately 100 millisecond sync-up operation is typically required to sync-up the spindle motor to permit monitoring of its spin-rate. Once the spindle motor spin-rate has been detected and the sync-up operation is completed, a back electromotive force (BEMF) spin-up operation begins at the approximately 400 RPM spin-rate to spin-up to an operating spin-rate, such as 5,400 or 7,200 RPMs. The BEMF spin-up operation monitors the BEMF of the spindle motor to thereby monitor the spin-rate of the disks. After reaching the operating spin-rate, the spin-up operation is finished and control is handed off to the run mode operation of the spindle motor.
As can be seen by the above discussion, the cogging operation takes up a substantial portion of the spin-up operation in the disk drive. Furthermore, in the case of ramp load operations, there is no head on media friction during the spin-up operation. In this case, the cog operation can oscillate for many seconds without the damping effect provided by the head on the disk media.
For the reasons stated above, there is a need to reduce the spindle motor spin-up time in a disk drive. In particular, there is a need to reduce the time to perform the cog operation, which prepositions the rotor prior to the spin-up of the spindle motor.
The invention can be regarded as a method of spinning-up a spindle motor to an operating spin-rate during a spin-up operation in a disk drive. The spindle motor has a plurality of windings and a rotatable rotor. The method includes the step of applying a voltage across at least one of the windings to cause the rotor to rotate. The rotating rotor induces a BEMF having a polarity across each of the windings. The method also includes the step of removing the applied voltage across the windings. The method subsequently detects the polarity of the BEMF in each of the windings to generate a previous multi-bit sequence representing a previous phase position ({circumflex over (xcex8)}n) of the rotor. The method then detects a change in the polarity of the BEMF in one of the windings to generate a present multi-bit sequence representing a present phase position (xcex8n) of the rotor. The method uses the previous phase position ({circumflex over (xcex8)}n) and the present phase position (xcex8n) of the rotor for selecting an initial commutation state in a spin-up commutation sequence such that the voltage is sequentially applied across a selected combination of the windings in order to spin-up the spindle motor to the operating spin-rate.
The invention can also be regarded as a disk drive connectable to a power supply voltage. The disk drive includes a spindle motor having a plurality of windings and a rotatable rotor. The disk drive also includes a spindle motor driver connected to the windings and connectable to the voltage. The disk drive also includes a spindle motor controller for commanding the spindle motor driver to apply the voltage across at least one of the windings to cause the rotor to rotate. The rotating rotor induces a BEMF having a polarity across each of the windings. The spindle motor controller subsequently commands the spindle motor driver to remove the applied voltage across the windings. The disk drive also includes a detector for monitoring the BEMF in each of the windings while the voltage is removed across the windings. The detector performs the steps of detecting the polarity of the BEMF in each of the windings to generate a previous multi-bit sequence representing a previous phase position ({circumflex over (xcex8)}n) of the rotor and detecting a change in the polarity of the BEMF in one of the windings to generate a present multi-bit sequence representing a present phase position (xcex8n) of the rotor. The spindle motor controller is responsive to the previous phase position ({circumflex over (xcex8)}n) and the present phase position (xcex8n) of the rotor for selecting an initial commutation state for commanding the spindle motor driver to initiate a spin-up commutation sequence starting from the selected initial commutation state such that the voltage is sequentially applied across a selected combination of the windings in order to spin-up the spindle motor to an operating spin-rate.